1. Field of the Invention
The present invention generally relates to a shock wave curing apparatus for applying shock wave pulses to a calculus to be disintegrated. More specifically, the present invention is directed to such a shock wave curing apparatus capable of correcting phase shifts contained in echo pulse signals reflected from a calculus within a biological body under medical examination by envelope-detecting these echo pulse signals.
2. Description of the Prior Art
To disintegrate, or destroy a calculus (stone) located within a biological body under medical examination, e.g., a patient, shock wave disintegrating apparatuses have been utilized and known as a "shock wave curing apparatus". In the typical shock wave curing apparatus, ultrasonic pulses having low energy are first applied to a calculus located on a focal point of a shock-wave pulse applicator before shock wave pulses produced by ultrasonic pulse having high energy are applied to destroy this calculus. As a result, since echo pulses with relatively high levels are reflected from this calculus and received by the ultrasonic pulse applicator, a decision can be made that there is a calculus to be disintegrated. Thereafter, the ultrasonic pulses with such high energy are applied to produce the shock wave pulses from the shock-wave pulse applicator. These shock wave pulses are transmitted to the calculus to be disintegrated.
Referring now to FIGS. 1, 2A, and 2B, the typical operation of the conventional shock wave curing apparatus will be explained.
In the circuit block arrangement of this conventional shock wave curing apparatus shown in FIG. 1, a shockwave pulse applicator 1 is employed. The shock wave pulse applicator 1 is arranged by a plurality of transducer elements. This shockwave pulse applicator 1 is selectively energized by a high-voltage power source 3 and a low-voltage power source 4 via a pulser 2 in order to selectively apply shock wave pulses and ultrasonic pulses, respectively. The shock wave pulses are applied to destroy a calculus (not shown in detail) positioned at, or near a focal point of this shock wave pulse applicator 1, whereas the ultrasonic pulses are applied to check whether or not there is such a calculus by receiving ultrasonic echoes reflected from a body portion of this focal point. A sectional shape of this ultrasonic pulse applicator 1 is spherical.
When the pulser 2 is connected to the high-voltage power source 3, pulse signals having high amplitudes are produced from the pulser 2 and then supplied to the ultrasonic pulse applicator 1, so that shock waves are transmitted from this applicator 1 to the focal point area of the biological body (not shown in detail), at which the calculus is located and can be disintegrated. When the low-voltage power source 4 is connected to energize the pulser 2, ultrasonic pulses are transmitted from this shockwave pulse applicator 1 to this focal point area. As a result, there is such a calculus to be destroyed in this focal point area, echo pulses with relatively high levels are reflected from this calculus and received by this applicator 1 to produce echo signals with high signal levels.
The resultant echo signals are supplied to a signal receiving circuit 5. In this signal receiving circuit 5, these echo signals are first summed with each other by an adder 13 (see FIG. 2A). The added echo signal 14 is rectified by a full-wave rectifier 15. Thereafter, the rectified echo signal is processed in a gating circuit 17 and a peak detector 18 to obtain a peak level of the echo signals (see FIG. 2A).
The peak level of the echo signals is compared with a threshold level derived from a threshold level setting circuit 9 in an echo level judging circuit 6. Then, if the echo signals are received from the calculus, the resultant peak level of the echo signals becomes higher than the threshold level, so that the echo level judging circuit 6 judges that the calculus to be disintegrated is located at, or near this focal point of the shockwave pulse applicator 1. Accordingly, the high-voltage power source 3 is connected to the pulser 2 so as to transmit shock waves from the applicator 1 to this calculus, whereby this calculus can be destroyed.
In FIG. 1, an ultrasonic probe 10 is employed to scan the biological body under control of an ultrasonic imaging apparatus 11, so that a B-mode image of this scanned biological body is displayed on a TV monitor 8. An image of the above calculus may be displayed together with this B-mode image.
Various drawbacks of this conventional shock wave curing apparatus shown in FIG. 1 will now be explained with reference to FIGS. 2A and 2B.
FIG. 2A shows an internal circuit arrangement of the signal receiving circuit 5, and FIG. 2B illustrates waveforms of the echo signals.
That is, as shown in FIG. 2B, the echo signals 12 derived from the shock wave applicator 1 own phase shifts with each other with respect to a time domain of the echo signals. As a result of these phase shifts, the output signal 14 of the adder 13 has relatively low peak. In other words, as illustrated in FIG. 2B, since three peaks 12p-1, 12p-2, 12p-3 of these echo signals 12 are not coincident with each other at a time instant "t.sub.1 ", the level of the single peak "14p" does not become three times higher than the respective peaks 12p-1, 12p-2, 12p-3 of the echo signals 12. As a consequence, the output 16 of the full-wave rectifier 15 has a relatively low peak level.
Thus, the resultant echo level of the peak detector 18 does not become so high, as compared with the threshold level. In the worst case, there are some risks that the echo level judging circuit 6 would mistakenly judge "no calculus" even if a calculus is actually present at or near the focal point within the biological body. Furthermore, the special resolution of the conventional shock wave curing apparatus is lowered.